The present invention is directed to apparatus and methods for minimizing the risk of air embolism when performing a procedure in a patient""s thoracic cavity. A specific application of the invention is described in conjunction with devices and methods for repairing and replacing a mitral valve in a patient""s heart, however, the invention may be used in conjunction with any other procedure including repair or replacement of mitral, aortic and other heart valves, repair of septal defects, pulmonary thrombectomy, electrophysiological mapping and ablation, coronary artery bypass grafting, angioplasty, atherectomy, treatment of aneurysms, myocardial drilling and revascularization, as well as neurovascular and neurosurgical procedures.
Various types of surgical procedures are currently performed to investigate, diagnose, and treat cardiovascular diseases. Using current techniques, many of these procedures require a gross thoracotomy, usually in the form of a median sternotomy, to gain access to the patient""s thoracic cavity. A saw is used to cut the sternum longitudinally thereby allowing two opposing halves of the anterior or ventral portion of the rib cage to be spread apart. A large opening in the thoracic cavity is created through which the surgical team may directly visualize and operate upon the heart and other thoracic contents.
Surgical intervention in the heart generally requires isolation of the heart and coronary blood vessels from the remainder of the arterial system and arrest of cardiac function. The heart is usually isolated from the arterial system by introducing an external aortic cross-clamp through a sternotomy and applying the clamp to the aorta between the brachiocephalic artery and the coronary ostia. Cardioplegic fluid is then injected into the coronary arteries, either directly into the coronary ostia or through a puncture in the aortic root, to arrest cardiac function. In some cases, cardioplegic fluid is injected into the coronary sinus for retrograde perfusion of the myocardium. The patient is then placed on cardiopulmonary bypass to maintain peripheral circulation of oxygenated blood. Another method of arresting the patient""s heart is disclosed in U.S. Pat. No. 5,433,700, which is assigned to the assignee of the present application and is herein incorporated by reference. U.S. Pat. No. 5,433,700 describes an endovascular catheter system for establishing arrest of cardiac function. The endovascular catheter system does not require a gross thoracotomy and facilitates less invasive methods of performing cardiopulmonary procedures.
Once the patient is placed on cardiopulmonary bypass, various surgical techniques may be used to repair a diseased or damaged valve, including annuloplasty (contracting the valve annulus), quadrangular resection (narrowing the valve leaflets), commissurotomy (cutting the valve commissures to separate the valve leaflets), shortening mitral or tricuspid valve chordae tendonae, reattachment of severed mitral or tricuspid valve chordae tendonae or papillary muscle tissue, and decalcification of valve and annulus tissue. Alternatively, the valve may be replaced, by excising the valve leaflets of the natural valve and securing a replacement valve in the valve position usually by suturing the replacement valve to the natural valve annulus. Various types of replacement valves are in current use, including mechanical and biological prostheses, homografts, and allografts, as described in Bodnar and Frater, Replacement Cardiac Valves 1-357 (1991), which is incorporated herein by reference. A comprehensive discussion of heart valve diseases and the surgical treatment thereof is found in Kirklin and Barratt-Boyes, Cardiac Surgery, pp. 323-459 (1986), the complete disclosure of which is incorporated herein by reference.
The mitral valve, located between the left atrium and left ventricle of the heart, is most easily reached through the wall of the left atrium, which normally resides on the posterior side of the heart, opposite the side of the heart that is exposed by a median sternotomy. Therefore, in order to access the mitral valve via a sternotomy, the heart is rotated to bring the left atrium into an anterior position accessible through the sternotomy. An opening, or atriotomy, is then made in the right side of the left atrium, anterior to the right pulmonary veins. The atriotomy is retracted by means of sutures or a retraction device, exposing the mitral valve directly posterior to the atriotomy. One of the aforementioned techniques may then be used to repair or replace the valve.
An alternative technique for mitral valve access may be used when a median sternotomy and/or rotational manipulation of the heart are undesirable. In this technique, a large incision is made in the right lateral side of the chest, usually in the region of the fifth intercostal space. One or more ribs may be removed from the patient, and other ribs near the incision are retracted outward to create a large opening into the thoracic cavity. The left atrium is then exposed on the posterior side of the heart, and an atriotomy is formed in the wall of the left atrium, through which the mitral valve may be accessed for repair or replacement.
Using such open-chest techniques, the large opening provided by a median sternotomy or right thoracotomy enables the surgeon to see the mitral valve directly through the left atriotomy, and to position his or her hands within the thoracic cavity in close proximity to the exterior of the heart for manipulation of surgical instruments, removal of excised tissue, and/or-introduction of a replacement valve through the atriotomy for attachment within the heart. However, these invasive, open-chest procedures produce a high degree of trauma, a significant risk of complications, an extended hospital stay, and a painful recovery period for the patient. Moreover, while heart valve surgery produces beneficial results for many patients, numerous others who might benefit from such surgery are unable or unwilling to undergo the trauma and risks of current techniques.
A problem which occurs in conventional open-heart procedures is that air enters the heart during the procedure and must be removed from the heart after completing the procedure. Air which remains in the circulatory system after the heart is closed may produce air emboli which could travel to the brain and cause a stroke or death. Conventional de-airing techniques include mechanical manipulations and venting of the heart to remove air trapped in the heart. U.S. Pat. No. 5,370,631, for example, discloses an apparatus for de-airing the heart which includes a slotted-needle and a resilient bulb.
Carbon dioxide has been used to displace air in the patient""s thoracic cavity to help prevent air emboli. In animal studies, carbon dioxide has been shown to be as much as twelve times more soluble in blood than air. Thus, displacing air with carbon dioxide may be beneficial in reducing the harmful effects of gas emboli.
In open-heart procedures, carbon dioxide has been introduced into the thoracic cavity through the median sternotomy. Since the patient""s chest is open, the carbon dioxide in the chest cavity readily disperses out of the chest and, therefore, carbon dioxide must be continuously or periodically replaced, Ng and Rosen, xe2x80x9cCarbon Dioxide in the prevention of air embolism during open-heart surgeryxe2x80x9d, Thorax 23:194-196 (1968).
Thus, a problem with previous use of carbon dioxide in open heart procedures is that air is free to enter the open chest cavity and high carbon dioxide concentrations cannot be maintained in the chest cavity for extended periods of time without requiring continuous or periodic injection of carbon dioxide.
In accordance with the principles of the present invention, methods and apparatus for reducing the risk of air embolism when performing a procedure in a patient""s thoracic cavity are provided. In an aspect of the present invention an instrument delivery member is inserted into a patient""s thoracic cavity between adjacent ribs thereby forming a percutaneous intercostal penetration. The instrument delivery member has a gas outlet for injecting a gas, preferably carbon dioxide, into the patient""s thoracic cavity. The gas displaces air from the patient""s thoracic cavity thereby reducing the risk of air emboli. The instrument delivery member also has a throughhole sized to permit an instrument to pass therethrough.
The present invention is particularly useful when performing the mitral valve replacement and repair procedures described in U.S. patent application Ser. No. 08/485,600 and U.S. patent application Ser. No. 08/163,241 both of which are assigned to the assignee of the present application and which are incorporated herein by reference. The methods facilitate surgical intervention within the heart or great vessels without the need for a gross thoracotomy. The procedure is carried out through small incisions within intercostal spaces of the rib cage without cutting, removing, or significantly deflecting the patient""s ribs or sternum thereby reducing the trauma, risks, recovery time and pain that accompany conventional techniques. The devices and methods permit removal of tissue from the thoracic cavity and introduction of surgical instruments, replacement valves and the like into the thoracic cavity, to facilitate heart valve repair and replacement. The devices and methods facilitate replacement of a heart valve with various types of prostheses, including mechanical and biological prostheses, homografts, and allografts.
In a preferred embodiment of the present invention, the instrument delivery member includes a plurality of gas outlets which are angled toward the distal end to help retain gas in the patient""s thoracic cavity. In an alternative embodiment, the gas outlets are angled substantially perpendicular to the longitudinal axis of the instrument delivery member with the gas passing adjacent the distal end. A vacuum pump may also be provided for withdrawing air from the patient""s thoracic cavity or for capturing gas escaping from the patient""s thoracic cavity.
The concentration of gas in the patient""s thoracic cavity is preferably monitored so that a threshold gas concentration is maintained. When using carbon dioxide, the gas concentration is preferably at least 70% and more preferably at least 90% by volume. Alternatively, the air concentration may be maintained at no more than 50% and more preferably no more than 5% by volume. The humidity and temperature in the patient""s thoracic cavity are also preferably monitored to maintain a desirable humidity and temperature. The relative humidity in the patient""s thoracic cavity is preferably at least 10% and more preferably at least 50%. The temperature of the gas is also preferably maintained at a temperature below body temperature and preferably below 20 (degrees) C.
The pressure of the gas in the patient""s thoracic cavity is also preferably monitored and regulated. The gas pressure is preferably maintained at a pressure higher than the pressure outside the thoracic cavity to prevent air does from entering the thoracic cavity. When performing the procedure described in U.S. patent application Ser. No. 08/485,600, which is incorporated herein by reference, a number of instrument delivery members, such as cannulas or trocars, are inserted into the patient to perform a mitral valve procedure. The present invention provides seals at the instrument delivery members to prevent the escape of gas so that the pressure can be maintained in the thoracic cavity. Such seals are commonly used in laparoscopic procedures. Unlike laparoscopic surgery, however, the pressure in the thoracic cavity is not used to retract the thoracic cavity and, as such, the pressure in the thoracic cavity is kept between 1 and 14 mm Hg and more preferably between 1 and 10 mm Hg and most preferably between 1 and 8 mm Hg all of which are below the pressures used in laparoscopic procedures which are typically between 15 and 20 mm Hg.
In another aspect of the present invention, the instrument delivery member includes a gas inlet and a gas outlet positioned to receive gas issuing from the gas inlet. The gas passing from the gas inlet to the gas outlet preferably passes across the throughhole, and preferably transects the throughhole, to act as a gas shield which minimizes gas losses through the instrument delivery member. The gas shield advantageously permits the introduction of instruments through the instrument delivery member without significantly hindering use of instruments. The gas which is used for the gas shield may be any gas such as carbon dioxide or air. A blower, fan or compressor is coupled to the gas inlet and may also be coupled to the gas outlet for closed circuit circulation.
In yet another aspect of the invention, a vent is provided for venting gas from the left ventricle when performing a procedure on the patient""s heart such as a mitral valve repair or replacement. The vent includes first and second lumens and first and second outlets fluidly coupled to the first and second lumens, respectively. The first lumen and first outlet are used for injecting gas into the patient""s heart and for evacuating gas from the heart when the heart is being closed after the mitral valve replacement or repair procedure. The second lumen and second outlet are used for sampling gas in the patient""s thoracic cavity.
In a specific application of the vent, the vent is positioned in the left ventricle and a gas, such as carbon dioxide, is injected into the patient through the first lumen. The gas displaces air in the left ventricle so that when the heart is closed the presence of air is minimized to minimize the risk of air emboli. The gas is preferably injected into the heart using the temperature, pressure, humidity and gas concentration monitoring and control system described above. When the heart is closed, the first lumen and first outlet are used to evacuate gasses from the heart. The second outlet and second lumen are used to collect gasses in the thoracic cavity for measuring pressure, temperature, humidity, and/or gas concentrations. The second outlet is spaced apart from the distal end so that the measurements are not overly influenced by the gas being injected into the left ventricle through the first lumen and first outlet.
In yet another aspect of the invention, an enclosure is provided around the patient for providing a sealed operating space. A gas, such as carbon dioxide, is maintained in the sealed operating space so that air does not enter the patient""s cardiopulmonary system during a medical procedure. The enclosure includes a seal, such as a drape, which engages the patient and provides a substantially air tight seal. The enclosure includes arm pass-throughs which are used by the surgeon to perform the medical procedure in the enclosure. An advantage of the enclosure is that it may also be used in conventional open heart procedures since a gas environment is created around the patient.
The terms xe2x80x9cpercutaneous intercostal penetrationxe2x80x9d and xe2x80x9cintercostal penetrationxe2x80x9d as used herein refer to a penetration, in the form of a small cut, incision, hole, or the like through the chest wall between two adjacent ribs, wherein the patient""s rib cage and sternum remain substantially intact, without cutting, removing, or significantly displacing the ribs or sternum. These terms are intended to distinguish a gross thoracotomy such as a median sternotomy, wherein the sternum and/or one or more ribs are cut or removed from the rib cage, or one or more ribs are retracted significantly, to create a large opening into the thoracic cavity. It is understood that one or more ribs may be retracted or deflected a small amount and/or a small amount of intercostal cartilage may be removed without departing from the scope of the invention.
These and other advantages of the invention will become apparent from the following detailed description of the invention.